Mobile communications devices such as cellular telephones communicate with telephones and computer systems using analog or digital signals at various stages of the signal transmission path. The conversion of the analog signals to the digital signals, and vice versa, is accomplished using analog-to-digital and digital-to-analog converters. The compression of speech signals is accomplished using one of several speech (and audio) coding standards.
Some of the more important coding standards include the North American cellular standards (e.g., IS54), the ITU-T standards G.723, G.728 and G.729, and the European cellular standards (GSM-EFR, GSM-FR and GSM-HR). The speech processing specifications of GSM are described, for example, in the GSM 6.01-6.32 Recommendation Specification document or in the book by Michel Mouly and Marie-Bernadette Pauter entitled The GSM System for Mobile, Communications, Palaiseau, France, ISBN 2-9507190-0-7.
Typically, these coding standards include various algorithm specifications that define how data must be manipulated so that the data conforms to the coding standard. For example, GSM is specified in a bit-exact standard that defines in detail all arithmetic operations and their required accuracy. Thus, each implementation that follows the standard will produce the same output for a given input sequence. By providing a collection of test vectors as part of the standard, compliance with GSM is easily verified.
As a result of strict specifications such as this, a given data operation may need to be implemented differently depending on the standard being applied. For example, a multiple-precision multiply operation that shifts the bits in a data word fifteen bits to the right is specified as a shift right fifteen bits operation in GSM-HR, but is specified as a shift right sixteen bits and a shift left one bit operation in GSM-EFR.
Conventionally, coding processing systems are implemented and configured for a single coding standard. That is, a given system cannot be dynamically switched between different coding standards. Thus, to provide the appropriate decoding for different coding standards, more than one coding system is required. This can significantly increase the cost to a user should he or she need to upgrade his or her system to support a different coding standard.
Thus, a need exists for a coding processing system that can conveniently and economically process signals defined according to a variety of coding formats.